Hydraulic vehicle brake systems are known that are in the form of external force brake systems and that comprise, besides a muscle power operated master brake cylinder, to which wheel brakes are hydraulically connected and that provide the pressure and volume for actuating wheel brakes, a further, electrically controllable pressure and volume providing device, which activates the wheel brakes in a “brake-by-wire” operating mode. In the event of failure of the electrically controllable pressure and volume providing device, operation of the wheel brakes is carried out solely by the muscle power of the driver of the vehicle.
Thus, for example, an electrohydraulic brake system with a brake pedal operated master brake cylinder, a travel simulator and an electrically controllable pressure providing device are known from WO 2011/029812 A1. The wheel brakes are subjected to pressure by the pressure providing device in a “brake-by-wire” operating mode. In a fallback mode, the wheel brakes are subjected to the pressure applied by the driver by means of the master brake cylinder that is operated by the brake pedal. It has proved disadvantageous with the brake system that in the event of a failure of the actuation or the drive of the pressure providing device, operation of the wheel brakes is only possible by the driver.
An electrohydraulic “brake-by-wire” brake system with a brake pedal actuated master brake cylinder, a first electrically controllable pressure providing device and a second electrically controllable pressure providing device are therefore described in WO 2012/150120 A1.
A pressure and volume boost of the brake pedal operation that is applied by the driver of the vehicle can be carried out by means of the second pressure providing device if the first pressure providing device fails.
Motor vehicles are to an increasing extent fitted with an environment sensor system, using which an environment control unit can determine a target trajectory for the vehicle and can actuate the drive, brake system and steering of the vehicle independently of the driver. The object thereof is automated driving, during which the vehicle is automatically maneuvered independently of the steering, drive or braking demands of the driver. During this an increase in operating safety, in particular of the brake system, is necessary even in the event of faults.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.